Go to UCM61xx Web GUI, click on PBX->Extensions, and edit one extension account. Enter number on “CallerID Number” and enter names on “First Name” and “Last name”.

Click on VoIP Trunks, edit SIP Trunk. Disable “Keep Trunk CID”.

Under the Advanced tab, empty the "From User" field.

Supplementary Notes:

If you are behind NAT and your Trunk is showing "Registered" at SIP.US, but it is registered to a private IP Address you will need to navigate to "PBX" ---> "SIP Settings" ---> "- NAT" and input your external IP Address in the "External Host" field. You must also put your local network address in the "Local Network Address" field.